# Noob: UI for many-to-many with has\_many :through

**URL:** <https://www.ruby-forum.com/t/noob-ui-for-many-to-many-with-has-many-through/133224>\
**Category:** Rails\
**Created:** [March 29, 2008, 12:19am UTC](https://www.ruby-forum.com/t/noob-ui-for-many-to-many-with-has-many-through/133224 "2008-03-29T00:19:15Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![rpardee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rpardee](https://www.ruby-forum.com/u/rpardee)\
**Post date:** [March 29, 2008, 12:19am UTC](https://www.ruby-forum.com/t/noob-ui-for-many-to-many-with-has-many-through/133224/1 "2008-03-29T00:19:15Z")

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Hey All,

I’ve got People and Projects, both of which has\_many :through =\>  
PeopleProjects. PeopleProjects has just one attribute of its own right  
now: role (which takes values like ‘programmer’, ‘project manager’  
etc.). I believe the models are doing what I need them to–I can add  
people to projects (and vice-versa) at the console.

But now I need to add that capability to my views. I’m imagining  
something like 2 list boxes, one listing everyone not (yet) assigned to  
the project, and the other listing people who _are_ assigned to it. On  
this imaginary page I can drag people from one box to the other, and for  
those who are assigned to it, easily designate their role with a  
drop-down. Of course I’ll settle for check boxes & submit buttons for  
managing each list if need be.

I’m assuming there’s no do\_what\_roy\_wants helper for this, so can  
anybody point me at tutorials or helpers that _do_ exist that should  
help me set something like this up? Or if it’s just not possible w/out  
mind-bending Nth-level rails mage skillz, then let me know that.

Thanks!

-Roy

Roy P.  
Research Analyst/Programmer  
Group Health Center For Health Studies (Cancer Research Network)  
(206) 287-2078  
Google Talk: rpardee

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<div class="post-metadata">

**Author:** ![rpardee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rpardee](https://www.ruby-forum.com/u/rpardee)\
**Post date:** [April 1, 2008, 1:22am UTC](https://www.ruby-forum.com/t/noob-ui-for-many-to-many-with-has-many-through/133224/2 "2008-04-01T01:22:28Z")

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Roy -

I had to solve a similar problem this morning with users and mailing  
list subscription, where the subscription may have additional parameters  
that need to be tracked.

If you take this from the perspective of your People -\> Edit view, then  
you should be able to include something like this to display a series of  
checkboxes showing each project - having it checked if this user belongs  
to that project:

```
 <% for proj in Project.find(:all, :order => :name) %>
    <%= check_box_tag "people[project_ids][]", proj.id, 

```

@people.projects.include?(proj), {:id =\> “people\_project\_#{proj.id}”} %\>  
\<%= proj.name %\>  
\<% end %\>

Then in your people\_controller.rb, for the ‘update’ action:  
def update  
@people = People.find(params[:id])  
@people.project\_ids = params[:people][:project\_ids]  
@people.update\_attributes(params[:people])  
if @people.valid?  
flash[:notice] = “Updated”  
redirect\_to :action =\> ‘index’ and return  
else  
render\_action ‘edit’  
end  
end

The key is that in your People model (people.rb), you need to set the  
attr for storing ‘project\_ids’, and create an after save method for  
ensuring that the relationships are updated properly:

```
attr_accessor :project_ids
after_save :update_projects

# After_save callback to handle mailinglist_ids
def update_projects
    unless projects_ids.nil?
        self.people_projects.each do |p|
            # delete the existing records if they're not in the 

```

array of ids to keep  
p.destroy unless  
projects\_ids.include?(p.project\_id.to\_i)  
project\_ids.delete(p.project\_id.to\_i)  
end  
# now build up the new associations  
project\_ids.each do |p|  
self.people\_project.create(:project\_id =\> p) unless  
p.blank?  
end  
reload  
end  
end

Hope that helps,

Richard Luck  
DiMax, Inc.  
Google Talk: dimaxinc

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<div class="post-metadata">

**Author:** ![rpardee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rpardee](https://www.ruby-forum.com/u/rpardee)\
**Post date:** [April 1, 2008, 11:14pm UTC](https://www.ruby-forum.com/t/noob-ui-for-many-to-many-with-has-many-through/133224/3 "2008-04-01T23:14:22Z")

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Very helpful–many thanks!